Perforin triggers iron-induced mitochondrial damage to drive ferroptosis and anti-tumor immunity.

Cytotoxic CD8+ T cells and natural killer cells are critical effectors of anti-tumor immunity. Cytotoxic lymphocytes eliminate tumor cells by releasing perforin (Prf1), a pore-forming protein that enables granzymes (Gzms) to enter target cells and trigger both caspase-dependent and -independent cell death. Here, we uncover a previously unrecognized, Gzm-independent function of Prf1. We find that Prf1 directly induces tumoral ferroptosis, an iron- and lipid-dependent form of cell death. Mechanistically, Prf1-mediated pore formation drives endocytosis of the transferrin receptor, which increases cellular iron uptake. Prf1 promotes the formation of endosomal-mitochondrial contacts, which leads to mitochondrial iron accumulation, mitochondrial dysfunction, and tumor cell ferroptosis. Dietary iron supplementation suppresses tumor progression in murine tumor models in a Prf1-dependent manner. Higher Prf1 expression correlates with improved survival and enhanced response to immune checkpoint blockade in patients with cancer. These findings define a Gzm-independent function of Prf1 as a direct executioner of cancer cell death through ferroptosis.